1. Field of the Invention
The present invention relates to an observation apparatus.
This application is based on Japanese Patent Application No. 2007-313546, the content of which is incorporated herein by reference.
2. Description of Related Art
Some existing conventional microscopes to observe fluorescence emitted from a sample have comprised, for example: a device for placing the sample and the optical system into a dark box; with a mechanism which, when the lid of the dark box is opened, halts irradiation of light onto the sample as well as protecting the observer from harmful light. That is to say, a contrivance which controls irradiation of light onto the sample by linking with the opening/closing movement of the lid of the dark box, has been invented (for example, refer to Japanese Unexamined Patent Application, Publication No. 2004-245979).
This microscope of Japanese Unexamined Patent Application, Publication No. 2004-245979 comprises an epifluorescent light source which irradiates excitation light of a specific wavelength band onto a sample placed on a stage, wherein fluorescence that has been radiated from the sample with use of the excitation light is used for image formation in the optical system and observation. In addition, the microscope also comprises: a box-shaped light shielding member which covers the whole or a part of the fluorescence microscope to prevent incidence of external light onto the sample; a lid which opens/closes an opening provided in a part of the light shielding member; an open/close detection unit which detects the open/close state of the opening defined by the lid; a shutter which opens/closes an optical path from the epifluorescent light source to the sample; and a control circuit which controls the driving of the shutter on the basis of an output signal from the open/close detection unit. The control circuit is designed to control the shutter so as to allow light from the epifluorescent light source to pass through when the opening is closed, and to shield against the light from the epifluorescent light source when the opening part is opened.
However, in cases where faint light is to be detected, particularly such a case where luminescence from living cells is observed, highly sensitive photodetector and imaging device such as a photo counting unit using PMT (photomultiplier tube) and EM-CCD (electron multiplying charge-coupled device) are often used. In such highly sensitive photodetector and imaging device, once strong light has been received, many electric charges may be accumulated in the device or detection circuit and it may take a long time to discharge these electric charges. For example, in a photo counting unit using PMT, after strong light has been received, it may take several dozens of minutes to discharge electric charges. Moreover, in EM-CCD, once strong light has been received, previous electric charges remain in the following image data that will be taken out later, which leads to a disadvantage in that the light signal is left in the image data which is supposed to be dark.
For example, in cases where an observation apparatus in which a sample serving as an observation target and an optical system and an imaging device (EM-CCD) for detecting the image (light) thereof are covered with a dark box to prevent incidence of external light, is used to observe changes in the amount of luminescence while culturing the sample, for example, for several days; the sample, the optical system, and the imaging device can be usually set in a dark state in the dark box. However, the lid of the dark box has to be opened sometimes for an operation such as agent injection into the sample. Such a case brings about a problem in that the image data shows incorrect values after the lid has been opened, and a problem in that the background which is supposed to be dark turns to be a bright image.